From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-ed1-f41.google.com (mail-ed1-f41.google.com [209.85.208.41]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 790002E64C; Tue, 28 May 2024 18:16:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.208.41 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1716920200; cv=none; b=frrFtK7uylhpCpY7l+3TP6eWGimBdrZEMO0uAWadIOxEHtopmjvSUFZsUoCSn2b7WOGmU+H73l6lV1ogDVtrVxAsr4xkckzxfszlRSQqjC9vvAHVPaIFfkuKQLzYadZO40pXnilrJq8m73WAyRS7qOPISCeVcSLvhjGv0Zhy6V0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1716920200; c=relaxed/simple; bh=1uRESX6KymYG8m8CUzqHk9mV+NXOdIDmZXgfbN7q8Us=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=lUqQi4O2eVPY4gxMj/cV0BgW02FBP8RWNoaMduAjmRU/xdi/hK5akF4BXusvtO21ldrBMyY0NYu6iErfRZazsT7x3WvTI+SlQ8gQ8L24hpBRSgVN/WJYg6iDDQbGvc4UoOsy6/+U+VUQ1Nou1dtGFHfALi/UsPI3F9cXHQjXkCs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=PDGn4m4r; arc=none smtp.client-ip=209.85.208.41 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="PDGn4m4r" Received: by mail-ed1-f41.google.com with SMTP id 4fb4d7f45d1cf-5789733769dso109894a12.1; Tue, 28 May 2024 11:16:38 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1716920197; x=1717524997; darn=vger.kernel.org; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=R++hvr7nzebtIxTs2CU6HsOf5klg6lcgJyuQ+SjZMnE=; b=PDGn4m4rH47SYgQrlVmr0x8XIT8fWWW9pcBx7GeBzFcsXxto6Ar70xaKIizDiCU8bD sJ3O2UvzdFFB/KWWCaBRUWpePZl4aUMFR48bMfL8v/o0t4SPYHoeX77p2Rp8rS3tiQdw anMFBcEjCQPvMLDOcIzC71YsASgLs+ZuiAAWAtOsWeytGEvXw5flKroABTVuWaVNgC4J Nb47LSjFFnP++9c+se693yuFimoji5p/7c+YdbIAxLUFiD85KjvpyhAxuahDl+D+CtjW 9E8N3DDyH+A+APK8NOPDL1U9mpUrfTMmSb/1sqCBfgNwRNDTS2Prvr8yP/K1pLn0IQox SWWQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1716920197; x=1717524997; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=R++hvr7nzebtIxTs2CU6HsOf5klg6lcgJyuQ+SjZMnE=; b=YjGvZf1hjuODKLYaOQ/skc7ZmG1ntqJFy0BAXDMHB5MDisB3W6yArSOV2t9CIlXtHh 8jOMAaIj91pFi8vODt1jy5zke3hXNZ221HuICl2eOvw5V6VM1UihxhtId1SgKSUSqObF YxzlA5GjKF4eqosTZZWyi0hJ0eE46xyG97hJL6qdFXN9CmYsawpYrUwYWDT8Y5xZaYJA JGUDVd4pGkOCJIvAa3TFFjkPv1sm8e8wRGxnX+gqp8xLtXKvkkvxqdBgaV99Yw3NHjgu 2Iuuob5nMgYKvyp4WyNHXpWezuTf5Ir1AYT/2lnNDEHTPh203nr93q4mS1xgcEBX1FUk g24Q== X-Forwarded-Encrypted: i=1; AJvYcCVgG9qOV5hYTt5occb2JeOYnmpEOqAMjk3ZB0nZGig2cClmmhzParJVZWdViPS5CRiWjLsQfVI9EXJjmzt6hQpKsFVCFWkk83WdSZomdGJOIn6NTMhl2bNwSBGOxnPuiEJnAQdbK/s/qLY7mE495zlhPuqANj/WQ0bsGV8SFp2LWZXSSw== X-Gm-Message-State: AOJu0YwINaMlUR4g8o/jYwE4Obd7MPB+X6I1v0FQOx0y8nXjkD631WCN cPjl0kPGFpP1vlFLdIiQS3gLgFlRW6RTauGeOSVr+flnfQjxJjsD X-Google-Smtp-Source: AGHT+IHHlxn9HQL0alkg34k8cLrkz+dMOEar28FIIBD1BfkeQ51ARQuTKg6QUl77or34Ks1j6M/LsA== X-Received: by 2002:a17:906:d799:b0:a62:196e:ef45 with SMTP id a640c23a62f3a-a623e8f6f57mr1424154366b.19.1716920196587; Tue, 28 May 2024 11:16:36 -0700 (PDT) Received: from andrea ([151.76.32.59]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-a62c501e85dsm394788766b.117.2024.05.28.11.16.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 28 May 2024 11:16:36 -0700 (PDT) Date: Tue, 28 May 2024 20:16:31 +0200 From: Andrea Parri To: Alexandre Ghiti Cc: Jonathan Corbet , Paul Walmsley , Palmer Dabbelt , Albert Ou , Peter Zijlstra , Ingo Molnar , Will Deacon , Waiman Long , Boqun Feng , Arnd Bergmann , Leonardo Bras , Guo Ren , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, linux-arch@vger.kernel.org Subject: Re: [PATCH 1/7] riscv: Implement cmpxchg32/64() using Zacas Message-ID: References: <20240528151052.313031-1-alexghiti@rivosinc.com> <20240528151052.313031-2-alexghiti@rivosinc.com> Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240528151052.313031-2-alexghiti@rivosinc.com> > + asm goto(ALTERNATIVE("nop", "j %[zacas]", 0, \ > + RISCV_ISA_EXT_ZACAS, 1) \ > + : : : : zacas); \ > + \ > __asm__ __volatile__ ( \ > prepend \ > "0: lr" lr_sfx " %0, %2\n" \ > " bne %0, %z3, 1f\n" \ > - " sc" sc_sfx " %1, %z4, %2\n" \ > + " sc" sc_cas_sfx " %1, %z4, %2\n" \ > " bnez %1, 0b\n" \ > append \ > "1:\n" \ > : "=&r" (r), "=&r" (__rc), "+A" (*(p)) \ > : "rJ" (co o), "rJ" (n) \ > : "memory"); \ > + goto end; \ > + \ > +zacas: \ > + __asm__ __volatile__ ( \ > + prepend \ > + " amocas" sc_cas_sfx " %0, %z2, %1\n" \ > + append \ > + : "+&r" (r), "+A" (*(p)) \ > + : "rJ" (n) \ > + : "memory"); \ With this, a cmpxchg32() will result in something like amocas.w.rl a5,a4,(s1) fence rw,rw (cf. my remarks in patch #4); this will/should provide enough sync, but you might want to try the alternative and currently more common mapping for "fully-ordered AMO sequences", aka amocas.w.aqrl a5,a4,(s1) Similarly for cmpxchg64 and other sizes. Andrea